It is increasingly clear that pathways of transcription regulation in eukaryotes exploit the structural proteins that package DNA into chromatin. A number of transcriptional regulators have been found to function at least in part by modifying chromatin. This includes previously identified protein complexes such as general transcription factors and novel protein complexes identified by genetic screens or by their activity in modifying chromatin in vitro. We have purified several histone acetyltransferase complexes from yeast and found that they contain a number of proteins previously implicated by genetic studies as functioning in transcriptional regulation. In addition, we have studied the yeast SWI/SNF complex, which is a member of a class of protein complexes that utilize the energy of ATP-hydrolysis to alter nucleosome structure and/or position. Both the HAT complexes and SWI/SNF contain a number of subunits that are homologues of human proteins implicated in the development of cancer, including tumor suppressor and proto-oncogenes (for example, Ini1, Moz, TRRAP, p33-ING1). Thus, the discovery and analysis of these complexes advances our understanding of human disease. The goal of this project is to biochemically analyze the functions of the yeast SWI/SNF complex and the SAGA and NuA4 histone acetyltransferase complexes which are able to function in transcription activation in vivo and in vitro. This proposal will analyze the recruitment of these complexes to promoters by DNA-binding transcription activators and their binding and retention on promoter nucleosomes. Experiments described in this proposal will investigate the functional links between the histone acetyltransferase complexes and SWI/SNF. In addition, these studies will also analyze how histone deacetylase complexes counteract the functions of SAGA, NuA4 and SWI/SNF. Finally, we will investigate mechanisms by which SWI/SNF may act in concert with histone deacetylases to facilitate transcriptional repression.